The present application claims priority from copending Canadian application No. 2,306,311, which is incorporated herein by reference.
The present application concerns parallel passage adsorbent and catalyst structures, particularly for high frequency pressure swing adsorption processes for separation of gas components or gas phase chemical reactions.
As outlined in co-pending U.S. patent application Serial No. 60/100,091 and U.S. Pat. No. 5,082,473, which are incorporated herein by reference, gas separation by pressure swing adsorption (PSA) is advantageously conducted at high cycle frequencies using laminated parallel passage adsorbers. These xe2x80x9cadsorbent laminatexe2x80x9d adsorbers provide high surface area and low pressure drop, which enable high frequency operation. The adsorbent is supported in thin sheets separated by spacers which establish the gap height between adjacent sheets and thus define flow channels between each pair of adjacent sheets.
One embodiment of a disclosed method for forming an adsorbent sheet for use in a pressure swing adsorption process comprises providing a metal support and depositing adsorbent material onto the support by electrophoretic deposition. The adsorbent material may be a variety of materials including, without limitation, a zeolite or a desiccant. Typical zeolites include hydrophilic zeolites and hydrophobic zeolites, such as A-type zeolites, X-type zeolites, Y-type zeolites, chabazite and silicalite. The support material typically is aluminum, steel, stainless steel, or alloys thereof.
The method also can include pretreating a surface of the metal to facilitate bonding of the adsorbent material to the support. For example, pretreating may comprise oxidizing the surface prior to depositing the adsorbent material. If the metal support is an aluminum support, the support may be anodized to form an alumina layer.
The adsorbent material is deposited on the support to form an adsorbent coating having a thickness of from about 5 to about 100 microns, and more typically from about 25 to about 60 microns. Adsorbent material has been deposited on a first planar surface, and on both first and second planar surfaces of the support material.
Electrophoretic deposition generally involves forming an electrophoretic deposition bath comprising an adsorbent material, and thereafter moving a support through the bath to deposit adsorbent on the support to form a coated support. The coated support may be fired to activate the adsorbent.
Adsorbent material may be deposited on plural strips, which are then assembled into an adsorbent laminate structure. In these embodiments, the first adsorbent material may be the same as or different from the second adsorbent material. For example, the adsorbent material may be a zeolite, or a combination of materials may be used, such as a using both a desiccant and a zeolite.
Laminates for use primarily in pressure swing adsorption processes also are described. One example of a disclosed laminate comprises an elongate support, such as a wire mesh support, which supports a first strip having a first adsorbent material applied thereto, and a second strip having a second adsorbent material applied thereto, where the first adsorbent is the same as or different from the second adsorbent. Typically, plural strips are positioned adjacent one another along the support. The strips may be spaced along the support to define a ventilation gap.
Flow channels allow gas flow about the laminates. For disclosed embodiments, the flow channels are from about 10 centimeters to about 20 centimeters long, and have a channel gap height of from about 50 to about 75 microns. The adsorbent material applied to the strips typically has an adsorbent layer thickness of from about 25 to about 60 microns. The laminates also typically have an adsorber voidage ratio of from about 0.25 to about 0.6, and for higher cycle frequencies an adsorber voidage ratio of from about 0.4 to about 0.5. The dimensions and voidage ratios can differ from those stated for working embodiments and still be within the scope of the present invention.
Adsorbers also are described comprising first and second wire mesh sheets having adsorbent material deposited on a first major planar surface of the sheets. The first and second sheets are placed adjacent one another and spaced sufficiently to define a flow channel. Another embodiment of disclosed adsorbers comprises two or more wire mesh sheets with adsorbent material deposited on both first and second major opposed planar surfaces thereof. The sheets are spaced from each other, such as by using a spacer, to define a gas flow channel. For example, the spacer may comprise a photolithographically etched metal foil, a wire mesh, or one or more sheets may comprise spacers embossed on a surface thereof. The adsorber also may include ventilation gaps to provide ventilation between flow channels.